Hospitalized patients with pulmonary or cardiovascular health issues often require supplemental oxygen. Typically, supplemental oxygen is delivered to a patient from an oxygen source that is interconnected by tubing to a patient interface, e.g., a mouth piece or a mask. In addition, some patients require medicine, which is delivered to the patient in the form of aerosolized particles mixed with the oxygen by a nebulizer that is interconnected to the tubing and positioned between the oxygen source and the patient interface. “Gas” as used herein shall refer to the mixture of oxygen and medicine. Those of skill in the art will appreciate that the source may deliver compressed air, a mixture of helium and oxygen, or any other substance that is typically used for patient care.
One drawback of prior art breathing systems is that the patient often re-breathes exhaled gas which reduces the amount of medicine-rich gas that would otherwise be received or drawn in by the patient. To avoid this drawback, breathing systems often include an inlet check valve or similar device that prevents exhaled air from intermingling with the incoming or supplied gas. More specifically, the pressure of the exhaled gas is sufficient to close the inlet check valve so that exhaled gas is forced through vents or an outlet port located between the patient and the inlet check valve. Pressure generated by the patient's inhalation opens the inlet check valve which allows the patient to breath in the prescribed gas.
It is another drawback that breathing systems of the prior art often waste medicine. More specifically, the source of many breathing systems continuously output oxygen at a predetermined but variable mass flow rate and pressure. Thus, when the patient is not inhaling, i.e., during exhalation or during the dwell period characterized as the time between inhalation and exhalation, gas continues to be delivered. As a result, the oversupplied gas is vented through the outlet port and/or through mask vents. To account for this decrease in medicine delivery to the patient, health care providers typically increase the amount of medicine added to the incoming oxygen. In an extreme example, a healthcare provider will prescribe three times the required dosage to accommodate losses, which is wasteful and increases healthcare costs. One attempt to solve the problem of waste has been to incorporate a reservoir bag into the gas delivery system to capture the delivered gas when the patient is not inhaling and subsequently deliver the captured gas to the patient upon the next breadth, which reduces the amount of gas vented to atmosphere. When the patient does inhale, the gas stored in the reservoir bag is inhaled along with gas that is being continuously delivered by the supply source.
Often reservoir bags are thick-walled and made of a durable material to withstand damage associated with shipping, handling, and use. Thick-walled construction, however, affects the ability of the bag to inflate and therefore adversely affects the ability of the bag to capture excess gas. It follows that as the pressure required to inflate a thick-walled reservoir is greater than the pressure required to open the inlet check valve, the pressurized gas delivered to the patient during the dwell time will often flow to the mask only to be vented. Stated differently, the inlet check valve of many breathing systems may open without the reservoir bag being filled and the gas will vent to atmosphere through the outlet port or mask vents rather than filling the reservoir.
One ineffective response to this problem is to increase the pressure of the oxygen source, and thus the gas, to ensure the bag inflates. However, increasing the source pressure will amplify the wasteful effect if the reservoir bag does not inflate quickly. That is, the pressure of the system is directly proportional to the gas mass flow rate which in turn is directly proportional to gas losses through the outlet port when the inlet check valve inevitably opens. And, even if the higher pressure gas completely inflates the reservoir bag, eventually the pressure of the incoming gas will urge the inlet check valve open, which allows the gas to vent through the outlet port. As one of skill in the art will appreciate, losses will be greater than those experienced by a system operating at a lower pressure.
Another way to address the medicine waste issue is to vary the size of the opening of the outlet port. U.S. Pat. No. 5,613,489 (“the '489 patent”), which is incorporated herein by reference, is directed to an outlet port comprised of a selectively adjustable orifice that provides adjustable resistance to exhalation. As one of skill in the art will appreciate, the greater the resistance to exhalation, the greater the pressure within the housing, which keeps the inlet check valve closed when the patient exhales and during the dwell time. The adjustable orifice may also be used to control exhalation by producing a positive expiratory pressure (PEP) which enhances patient therapy. The orifice of the exhalation port described in the '489 is adjusted by altering a wedge-shaped opening from about 10 degrees to about 60 degrees. One drawback with this method of controlling exhalation is that a path is always open. Thus, if the system of the '489 patent is used with a self-inflating reservoir, as will be described in detail below, ambient air will be drawn in through the orifice when the patient inhales. That is, patients with poor lung function will not be able to provide enough negative pressure during inhalation to collapse a self-inflating reservoir, which maximizes medicine delivery, without the orifice leaking ambient air.
Accordingly, there is a long standing and unresolved need to provide a system for delivering medicine to a patient that efficiently stores a reserve of gas when the patient is not inhaling, thereby eliminating or substantially reducing medicine waste by making the reserve available to the patient when he or she subsequently inhales.